On the aniversary of the abolition of the slave trade, it's worth recalling that torture is inextricably linked to slavery. As Scott Horton explains more fully here, when Wilberforce and Wesley aimed to persuade the British elites that the slave trade was evil, they did not cite Biblical proscriptions against slavery. Why? Because the Bible is actually very ambiguous about slavery (the Southern Baptist Convention even used scripture to defend slavery in America). So Wilberforce stressed that the slave trade required unspeakable cruelty, abuse and torture of its victims. That was his rhetorical gambit. He framed his case against the slave trade as a case against inhumane treatment of prisoners of war. The print above was part of the abolitionist case and it was designed to show human beings whose dignity has been violated. The detail I find most arresting is that the small text explains how tightly packed the slaves were on the ship "in the manner of galleries in a church." Wilberforce was appealing to his fellow Christians. And he believed he could persuade them about inhumane treatment more easily than he could persuade them about slavery.
But the two were and are inextricable. Torture was necessary to maintain slavery. It was integral to slavery. You cannot have slavery without some torture or the threat of torture; and you cannot have torture without slavery. You cannot imprison a free man for ever unless you have broken him; and you can only forcibly break a man's soul by torturing it out of him. Slavery dehumanizes; torture dehumanizes in exactly the same way. The torture of human beings who have no freedom and no recourse to the courts is slavery.